1. Field of the Invention
The present invention relates to a noise elimination method and apparatus which eliminate noises included in various kinds of transmission data or reproduction data, in order to produce the reconstructed data without error.
The noise elimination method and apparatus of the present invention are applicable to various fields of technology. If a device for producing the reconstructed data from the received data signal is defined to be a modem in a broad sense, the present invention is applicable to modems of power-line-carrier communication systems, the xDSL modems including ADSL (asymmetric digital subscriber line) modems or etc., and modems of short-distance radio communication systems based on the standards IEEE 802.11a, IEEE 802.11b, etc. Moreover, the present invention is applicable to bar code readers which print and read the data with the scanner, and magnetic or optical disk devices which store and reproduce the data, and these devices are also a kind of the modem in the broad sense.
2. Description of the Related Art
Hereinafter, the power-line-carrier communication system will be described as an example of the communication system under highly noisy environment.
FIG. 18 shows a power-line-carrier communication system as the example of the communication system under highly noisy environment.
As shown in FIG. 18, the access node 102 is provided in the distributing substation 101, for example, in the power-line-carrier communication system. The optical fiber 103 from the access node 102 is installed along with the 6 kV high-voltage power line, and the high-voltage power line is linked with the transformer 105 on the utility-line pole. The transformer 105 serves to transform the 6 kV high voltage into 100V or 200V, and distribute the electricity through the low voltage power line 106 to each home.
The power line carrier modem 104 is provided at the location of the transformer 105, and the modem 104 performs modulation/demodulation and relaying of the data transmitted between the optical fiber 103 and the low-voltage power line 106.
The incoming line 107 from the low-voltage power line 106 is connected with the panel board 108 of each home. For example, at each home premises, the refrigerator 111, the facsimile apparatus 112, the air-conditioner 113, and the plug socket 110 are connected with the interior-distribution line 109 from the panel board 108. The modem 114 is connected to the plug socket 110 via the power cable, and connected to the personal computer 115 via the LAN (local area network) cable of 10 BASE-T.
In the above-described configuration, the transmission of the data between the modem 114 (connected to the personal computer 115) and the power-line carrier modem 104 is carried out by the power-line-carrier communication, and the transmission of the data between the power-line carrier modem 104 and the access node 102 is carried out by the optical fiber communication. This configuration makes possible the Internet connection of the personal computer 115 and the centralized control of the household-electric-appliance devices.
The commonly used installation is that the low-voltage power line 106 is connected with the incoming lines 107 to 30 houses, and the low-voltage power line 106 and the interior-distribution line 109, which are equivalent to the transmission line of the power-line-carrier communication system, usually have complicated transmission characteristics. Moreover, the inverter control composition of the various household-electric-appliance devices such as the air-conditioner 113 has increased, and the noise component which is included in the interior-distribution line 109 will become very large.
As for the transmission bandwidth of the power-line-carrier communication system, the kilohertz (kHz) band tends to be influenced by the impedance or the noise of the household-electric-appliance devices, and the band in that case is restricted to 450 kHz or less. Hence, the transmission speed of the kilohertz band becomes low. On the other hand, the allowance value of the leakage electric field for the megahertz (MHz) band is severe, and a part of the application area is restricted. However, using the wide band is possible, and the high-speed transmission of the megahertz band is possible.
Generally, it is considered that the spread spectrum (SS) communication is little influenced by the noise component. FIG. 19A, FIG. 19B, FIG. 19C and FIG. 19D show the concept of the spread spectrum communication.
FIG. 19A shows the outline of the transmitter unit and the receiver unit of the spread spectrum (SS) communication system. In the transmitter unit, the data modulation unit (DATA_MOD) 121 performs the digital modulation as a primary modulation of the information, such as the voice, the picture, the data, etc. The SS modulation unit (SS_MOD) 122 performs the SS modulation as a secondary modulation of the information with the SS code from the SS code generation unit (SS_CODE_GEN) 123. The SS modulation unit 122 transmits a data signal obtained by the SS modulation.
In this case, the data signal obtained by the spread spectrum modulation is modulated to the radio frequency, and it is transmitted from the antenna of the SS modulation unit 122. The antenna of the receive unit receives the data signal sent from the transmitter unit. In the receiver unit, the SS demodulation unit (SS_DEM) 124 performs the reverse SS demodulation of the received data signal with the SS code from the SS code generation unit (SS_CODE_GEN) 126. The data demodulation unit (DATA_DEM) 125 performs the digital demodulation of the data signal from the SS demodulation unit 124 so that the reconstructed data is produced.
FIG. 19B shows the configuration of the SS modulation unit 122 which is constituted by the multiplier 127, and FIG. 19C shows operation of the SS modulation unit 122 of FIG. 19B.
As shown in FIG. 19B, the digital modulation signal (a) of the amplitude of ±1 and the SS code (b) of ±1, both shown in FIG. 19C, are sent to the inputs of the multiplier 127, and the multiplier 127 performs the multiplication of the signal (a) and the signal (b), and outputs the SS modulation signal (c) which has the amplitude of ±1 shown in FIG. 19C.
FIG. 19D shows the power flux density for the frequency before the spreading on the left-hand side and the power flux density for the frequency after the spreading on the right-hand side. As shown in FIG. 19D, the power flux density of the SS modulation signal after the spreading is diffused over the frequencies in the wide range.
The practical specification of the power-line-carrier communication system to which the above-mentioned spread spectrum communication is applied is as follows: the transmission rate is 9600 bps, the transmitter unit using the primary modulation of DPSK (differentia phase shift keying) and the secondary modulation of DS-SS (direct spread-spread spectrum), and the receiver unit using the frequency band of 150–350 kHz, the band-division delayed detection of the primary and secondary demodulation, and the power flux density of 10 mW/10 kHz or less. The shape of the transmission power envelop is flat with respect to the frequency axis. The SS code is the mesa-type envelope generation code. The receiving sensitivity is 60 dB μV or less.
FIG. 20 shows a conventional modem to which the above-mentioned spread spectrum communication is applied.
In FIG. 20, reference numeral 131 is the differential coding unit (DIF_COD), reference numeral 132 is the SS modulation unit (SS_MOD), reference numeral 133 is the SS code generation unit (SS_CODE_GEN), reference numeral 134 is the digital-to-analog converter (DAC), reference numeral 135 is the band pass filter (BPF), reference numeral 136 is the amplifier (AMP), reference numeral 137 is the coupling unit, reference numeral 138 is the band pass filter (BPF), reference numeral 139 is the analog-to-digital converter (ADC), reference numerals 140-1 to 140-n are the band pass filters (BPF), reference numerals 141-1 to 141-n are the delayed detection units (DEL_DET), and reference numeral 142 is the multiplexer. Moreover, in FIG. 20, SD is the transmitting data signal, RD is the received data signal, CLK is the clock signal, and AC is the interior-distribution line of the alternating current.
In the transmitter unit of the conventional modem of FIG. 20, the differential coding unit 131 performs the differential coding of the transmitting data signal SD. The SS modulation unit 132 performs the SS modulation of the digital modulation signal by multiplication of the SS code from the SS code generation unit 133. The DAC 134 converts the SS modulation signal from the SS modulation unit 132 into the analog signal. The BPF 135 removes the undesired frequency component from the analog signal sent by the DAC 134. The amplifier 136 amplifies the data signal sent by the BPF 135, and sends out the amplified data signal to the interior-distribution line AC via the coupling unit 137 as the SS modulation signal. The coupling unit 137 includes the high frequency transformer, the capacitor, etc.
In the receiver unit of the conventional modem of FIG. 20, the BPF 138 removes the undesired frequency component from the received data signal received from the interior-distribution line AC via the coupling unit 137. The ADC 139 converts the analog signal sent by the BPF 138 into the digital signal. The ADC 139 divides the SS band into “n” frequency ranges. Each of the BPF 140-1 to 140-n has the center frequency of one of the “n” frequency bands as the pass-band frequency. Each of the BPF 140-1 to 140-n output the “n” signal components in the SS band.
Moreover, the delayed detection units 141-1 to 141-n perform the delayed detection of the signals sent by the BPF 140-1 to 140-n. The multiplexer 142 performs the multiplexing of the signal components sent by the delayed detection units 141-1 to 141-n, and outputs the received data signal RD and the clock signal CLK.
In the spread spectrum communication, the noise component is dispersed within the transmission band and included in the SS modulation signal. The correlation value of the SS modulation signal with the SS code becomes zero through the reverse SS demodulation process. Since the correlation with the SS code is taken, the SS communication system is little influenced by the noise component.
However, when it is applied to the power-line-carrier communication system, the characteristics of the transmission line are indefinite and vary. The noise, which is accompanied with the switching noise and the load fluctuation effect by the inverters, is included. There may be the case where the noise component is larger in amplitude than the signal component.
In such a case, even if the delayed detection of the received SS modulation signal is carried by using the frequency region correspondence, the influence by the noise component is large and it is difficult to produce the reconstructed data signal without error.
In order to overcome the above problem, Japanese Laid-Open Patent Application No. 2000-164801 discloses a noise elimination apparatus which enables high-speed data transmission of the power-line-carrier communication system without error by eliminating the noise from the received SS modulation signal.
FIG. 21 shows a conventional noise elimination apparatus disclosed by the above-mentioned document.
As shown in FIG. 21, the transmitting-signal point generating unit (TX_SIG_PNT GENE) 151 generates the signal point corresponding to the transmitting data signal. For example, suppose the case where the signal point as in the 4 phase modulation to the I axis and the Q axis is given as in (1) the data signal point.
Next, the zero-point insertion unit (Z_PNT INSERT) 152 inserts the zero point to the transmitting data signal. By the zero-point insertion, the zero point inserted appears at the center of the I-axis and the Q-axis of the transmitting data signal as in (2) the data+zero point.
The transmission path (TRANS PATH) 153 is the transmission line in the above-mentioned power-line-carrier communication system, and the transmission path 153 shows the noise spectrum in that case. As shown in FIG. 21, the noise component of 150 kHz or less is very large in the transmission path 153. Hence, the signal point will be in the unknown state due to the large-amplitude noise component so that the signal delivered through the transmission path 153 is as in (4) the data+zero-point+noise.
Then, the noise component which is overlapped at the zero point is extracted by the zero-point thinning unit (Z_PNT THINNING) 155. The noise component on the signal point is predicted by the interpolation prediction unit (INT_PRE) 156, and the noise component on the signal point is removed by the noise elimination unit (NOI_ELI) 154.
As in (5) the data signal point, the receiving signal point which is the same as (1) the data signal point can be obtained at the receiving signal point reproduction unit (RX_SIG_PNT REPR) 157. Hence, the receiving signal point reproduction unit 157 can produce the reconstructed data signal without error.
FIG. 22A, FIG. 22B, FIG. 22C and FIG. 22D show the noise elimination operation of the apparatus of FIG. 21.
In the zero-point insertion unit 152, zero is inserted at the signal points of the data signals S1, S2, etc. on the time axis, as in the transmitting zero-point insertion of FIG. 22A. When the transmission frequency is 192 kHz, the frequency of the zero-point inserted signal is doubled to 384 kHz by the zero point insertion.
As in the received signal of FIG. 22B, the noise components N1, N2, etc. are included at the data signals S1, S2, etc., and the noise components Na, Nb, etc. are included at the zero points between them.
The zero-point thinning unit 155 and the interpolation predicting unit 156 carry out the noise extraction and the interpolation prediction. As in the thinning and interpolation prediction of FIG. 22C, the noise components Na, Nb, etc. at the zero points are extracted, and the noise components N1, N2, etc. included at the signal points S1, S2, etc. are determined by the interpolation prediction processing by using the extracted noise components Na, Nb, etc.
Thus, as in the state after the noise removal of FIG. 22D, the data signal (S1, S2, etc.) can be obtained by eliminating the noise components N1, N2, etc. from the received signal of FIG. 22B. The noise components N1, N2, etc. are determined by the interpolation prediction processing as mentioned above.
The zero-point insertion can be performed in various manners. FIG. 23A, FIG. 23B, FIG. 23C, FIG. 23D and FIG. 23E show various methods of the zero-point insertion.
FIG. 23A shows the method of inserting a zero point for every three signal points. FIG. 23B shows the method of inserting a zero point for every two signal points. FIG. 23C shows the method of inserting a zero point for every signal point. FIG. 23D shows the method of inserting two zero points for every signal point. FIG. 23E shows the method of inserting three zero points for every signal point.
The effect of noise elimination becomes large as the number of the zero points inserted increases. However, the transmission frequency bandwidth becomes large as the number of the zero points inserted increases. Moreover, if the transmission frequency bandwidth remains unchanged, the transmission speed becomes low.
FIG. 24A shows the configuration of a modem to which the zero-point insertion is applied. FIG. 24B shows an example of the signal waveform of the modem of FIG. 24A.
In FIG. 24A, SD is the transmitting data signal, reference numeral 241 is the conversion unit (SCR S/P) which includes the scramble processing unit (SCR) and the serial/parallel conversion unit (S/P), reference numeral 242 is the code-conversion unit (G/N SUM) which includes the gray-code/natural-code conversion unit (G/N) and the code summing processing unit (SUM), reference numeral 243 is the signal point generating unit (SIG_PNT GENE) which generates the signal point based on the signal which is obtained through the serial/parallel conversion and the code conversion, reference numeral 244 is the roll-off filter (ROF), reference numeral 245 is the digital-to-analog converter (D/A), reference numeral 246 is the low pass filter and modulation unit (LPF MOD), reference numeral 247 is the band pass filter (BPF), reference numeral 248 is the transmitting clock generating unit (TX-CLK), and TX-line is the transmission line.
Moreover, in FIG. 24A, RX-line is the receiving line, reference numeral 251 is the band pass filter (BPF), reference numeral 252 is the demodulation and low pass filter unit (DEM_LPF), reference numeral 253 is the analog-to-digital converter (A/D), reference numeral 254 is the roll-off filter (ROF), reference numeral 256 is the timing extraction unit (TIM), reference numeral 257 is the phase synch oscillation unit (PLL VCXO), reference numeral 258 is the receiving clock generating unit (RX-CLK), reference numeral 259 is the equalization unit (EQL), reference numeral 260 is the carrier automatic phase-control unit (CAPC), reference numeral 261 is the decision unit (DEC), reference numeral 262 is the code conversion unit (DIF N/G) including the difference processing unit (DIF) and the natural-code/gray-code conversion unit (N/G), reference numeral 263 is the conversion unit (P/S DSCR) including the parallel/serial conversion unit (P/S) and the descramble processing unit (DSCR), and RD is the received data signal.
In the transmitter unit of the modem of FIG. 24A, the conversion unit 241 performs the scramble processing of the transmitting data signal SD, and converts the data signal after the scramble processing into the parallel data corresponding to the modulating-signal points. The code conversion unit 242 converts the gray code into the natural code, and performs the summing processing of the natural code such that the demodulation is possible without being influenced by the demodulation reference phase.
The signal point generating unit 243 generates the signal points in conformity with the modulating-signal points. The roll-off filter 244 removes the high-frequency components from the data signal. The D/A converter 245 converts the digital signal into the analog signal. The analog signal is passed through the low pass filter (LPF), and the resulting signal is inputted to the modulation unit (MOD) 246. The modulation unit performs the modulation of the input analog signal. The band pass filter 247 restricts the frequency of the modulated signal to the transmitting band. The resulting data signal from the band pass filter 247 is sent to the transmitting line TX-line.
In the receiver unit of the modem of FIG. 24A, the band pass filter 251 removes the undesired frequency component from the received data signal received through the receiving line RX-line. The data signal from the BPF 251 is sent to the conversion unit 252. In the conversion unit 252, the demodulation part (DEM) performs the demodulation of the received data signal, and the low pass filter (LPF) removes the high-frequency component from the demodulated signal. The A/D converter 253 converts the analog signal into the digital signal.
The digital signal is passed through the roll off filter 254 and sent to the equalization unit 259. The equalization unit 259 performs the equalization of the waveform of the received data signal. The carrier automatic phase-control unit 260 performs the phase adjustment of the received data signal. The decision unit 261 determines the data in the received data signal. The code conversion unit 262 performs the difference processing with respect to the summing processing performed by the transmitter unit, and performs the natural-code/gray-code transform processing. The conversion unit 263 converts the parallel code into the serial code, and performs the descramble processing of the serial code so that the reconstructed data is produced as the received data signal RD.
The modulation unit 246 includes the QAM (quadrature amplitude modulation) unit, such as the 64 QAM modulator, and the demodulation unit 252 includes the QAM demodulation unit, such as the 64 QAM demodulator. The portion of the modem, indicated by the dotted line in FIG. 24A, including the transmitting line TX-line and the receiving line RX-line, is constructed as the QAM path having the functions of the QAM modulation and demodulation.
As shown in FIG. 24B, the waveform of the signal indicates that, except for the peak points of the signal, the signal is transmitted at the transmission rate, the transmission rate corresponding to the Nyquist interval at which the zero point appears at the fixed period. The arrows in FIG. 24B indicate the data corresponding to the signal points where the amplitude of the signal is equal to the peak amplitude.
Various kinds of electrical machinery and apparatus are arranged in the domestic or home environment, and they are connected with the low-voltage interior-distribution line which is 100V or 200V. There has been proposed a home network which uses the interior-distribution line as the transmission line. The above-mentioned power-line-carrier communication system is applicable to the proposed network. Moreover, various kinds of sensors, such as a fire detection sensor making use of the detection of smoke, temperature, etc., a gas leakage detection sensor, and an intrusion detection sensor are arranged in the domestic or home environment. There has also been proposed to connect such sensors to the home network.
Furthermore, various kinds of home service systems which are described as in the following can be realized by using the home network and the low-voltage power line, which are connected to a certain service center via the radio circuits or the telephone line.
(a) The remote maintenance service system which performs remote maintenance and troubleshooting of the home devices.
(b) The mobile service system which is accessed from a portable telephone, etc. and performs remote monitoring and manipulation of the home devices.
(c) The energy service system which performs remote monitoring of the amount or the charge of the electricity used, and energy-saving operation control, etc.
(d) The living assisting service system which performs the centralized control and operation of the light-proof blind, the ventilating fan, and the lighting etc.
(e) The home health service system which is connected to the medial institution and performs health management and physical state management of elderly people.
(f) The security service system which performs fire prevention, the disaster prevention, the crime prevention, etc., by transmitting the detected information of the home sensors.
FIG. 25 shows the problems of various data transmission methods in the case of the home service systems.
As shown in FIG. 25, when the QAM (quadrature amplitude modulation), the SS (spread spectrum), the CDMA (code division multiple access), the MC (multiple carrier), and OFDM (orthogonal frequency division multiplex) methods are used as a means of data transmission, the possibility of high speed transmission, the influence of multiple path, the ease of waveform equalization, the influence of noises, low-cost production, and low power consumption become the subjects that have to be solved. Among these subjects, it is very important to solve the influence of the large-amplitude noise.
As mentioned above, the use of inverter control increases and the household-electric-appliance devices serves as the noise source by the inverter switching control. Moreover, the electrical machinery and apparatus which generate the electromagnetic waves, such as the electromagnetic-induction rice cooker, is increasing.
Therefore, when the home network is configured with such household-electric-appliance devices, the large-amplitude noise will be included in various kinds of data and the noise-included data signal will be transmitted.
In this case, although the interpolation prediction can be carried out and the noise on which the signal point is overlapped by inserting the zero point by the transmitting side and extracting the noise on which the zero point is overlapped can be removed, in the state where the device which inserts the zero point in the transmitting side has not spread, it is necessary to perform noise cancellation by the receiving side.
However, the data receiving processing which is carried out for the noise elimination when the large amplitude noise is included in the received data signal is not provided by the conventional noise elimination method.